Amplifying device



Jan. 8, 1935. A, B5 S ITH 1,986,984

AMPLIFYING DEVICE Filed July 18, 1932 9 InTeniFr HfihurBssse SW11 Patented Jan. 8, 1935 UNITED STATES amurmc navrcu Arthur Bessey Smith, Evanston, 111., assignor to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application July 18, 1932, Serial No. 623,076 11 Claims. (01. 179- 11) My invention relates to audible-frequency amplifiers in general, but, more particularly, it relates to electrically operated mechanical amplifiers of audible frequencies; andthe principal .6 object of my invention, briefly stated, is the provision of a new and improved mechanical amplifier which is particularlyv suitable for use in longytelephone lines, in paging systems, and wherever telephone speech current must be amplified. 6 :My. new and improved amplifier consists of an electromagnet mechanically connected to a mi crophone cell. The current to be amplified'passes through the coil, or coils, of the electromagnet and vibrates the armature and moves the electrode of the cell, which undulates the direct cur,- rent. By means of an induction coil or the equivalent, it sends out the electrical wave of increased power.

Acomplete understanding of the operation and construction of the amplifier of my invention may be had from a study of the detailed description, which follows, in conjunction with the associated drawing comprising Figs. 1 'to 6, inclusive, in which:

Fig. 1 is a diagrammatic representation ofthe amplifier circuit;

Fig. 2 is an enlarged view of the microphone cell employed;

Fig. 8 is a front elevation of the amplifier completely assembled;

Fig. 4 is a side elevation of the assembled amplifier with sufficient of the side frame structure removed to permit a clear view of the apparatus;

Fig. shows two views of the upper pole piece; and

. Fig. 6 is a perspective view of the lower pole piece.

With reference particularly to Figs. 3 to 6, the construction of the amplifier will be described. To the frame structure comprising the side pieces 1 and the end piece 2 are secured the two soft iron-brackets 3 and 4. Bracket 4, Fig. 6, is shaped from a piece of soft iron of suitable dimensions by bending the portion 5 at right angles to the surface of piece 4 and then bending the side flares 6 at right angles to the portion 5. The bracket 4 is then secured to the frame pieces 1 by means of. screws 17.

Secured to the side flares 6 by-means of screws 18.are the soft iron magnet cores 7 having the shape shown best in Fig. 3. Wound upon these cores 7 are the coils 8. Resting on the upper surface of portion 5 of bracket 4, Fig. 3, on a knife edge pivot, is the soft iron armature 10. This armature lies between the ends of cores '7 and is movable in either direction from the vertical.

The armature 10 must follow the alternations of the currenti flowing inthe coils 8 of the electween the core magnets.

tromagnet. Therefore, a polarized electromagnet must be used, since it is well known that the armature of a neutral electromagnet will vibrate at twice the frequency if the exciting current is strong enough. Consequently, the permanent magnet 11 is providedand secured to the brackets 3 and 4, which thereupon become the poles of the magnet. It will be assumed that with the permanent magnet in place the pole piece 4 is the north pole and the pole piece 3 is the south pole.

As far as I know, all of the polarized electromagnets madeand used at the present time have the characteristic-that the armature will be attracted to and stick to the nearer pole. If the armature is pushed to the other pole, then it will stay there. For many purposes this stickyf property is a great advantage.

When using polarized eleotromagnets in speech amplifying devices, the "sticky property is a serious handicap. Up to the present time, springs, known ascentering springs, have been used to overcome this property in order to maintain the armaturecentered between the two poles o! the magnet when no current is flowing through the magnet coils. This spring is necessarily stiff and introduces a strong tuning of the acoustic system. This tuning characteristic is inherent in the system.- and causes the devices to respond much more loudly to frequencies in the neighborhood of the resonant point than to frequencies higher. and lower. This causes distortion which cannot be evaded.

With a polarized electromagnet constructed as I have constructed the one for use in the present amplifier, distortion is eliminated and true and uniform amplification is obtained. I have discovered that the spring can be eliminated by using magnetic means'to; center the armature be- To accomplish this, the bracket 3 has been constructed from two bent stampings of soft iron, as shown best in Fig. 5-that is, having the extending portion 16 which is of substantially the same thickness as the armature 10. The bracket 3 is secured to the sides 1 of the frame by means of brass brackets 19 and screws 19' in such position as to leave a small air gap between the upper end of armature 10 and the extension 16.

The magnetic flux from the north pole of the permanent magnet 11 flows into the pole piece 4 and then divides, going through the two cores 7 and the armature 10. At the upper ends of the cores 7. the fluxes cross the air gaps and join the armature flux. From there, the, fiux crosses the air gap to the extension 16 of pole 3 and thence to the south pole of the permanent magnet. a

In this manner the armature 10 is strongly polarized by the permanent magnet, but only a relatively weak centering force is required since return of the armature to the center position-;.:. The strength of the centering force may be nicely controlled by shaping the face of ex'tensior'vlfiand the end face of the armatureto procurethe,

desired force. ,1 Y. i a 7 Because of the slight centering force of polarie zation, there is a very low natural ,frequency, but;

input'current being truly and greatly amplified ,by my: new and improved electro-mechanical it is so low that it is not a factor in 'thera'n'ge of audible frequencies.

My structure permits so proportioning the parts that there is considerable magnetic flux in the side air gaps (between electromagnetpoles and armature) This is desirable because the degree of control which the coils exercise over the armature depends upon the steady flux in those air gaps which are changed in" length during vibration. Itis desired to make this side-gap steady flux as strong as possible, without caus ing sticking of the armature. I I provide each magnet core with a verythin residual stop made of non-magnetic material to prevent actual contact of armature to mag-net poles (during handling, shipping, etc.).' Actual contact'causes sticking in some cases, but the residualmay be 'very thin, about 0.05 millimeter, not interferring with useful vibrations; Because of the thinness, the residuals have not been shown on the drawing;

Because it gives the most nearly correctreproduction of the incomingwave, I use the differential transmitter form of microphone cell and battery" circuit. The two cells 12" are so arranged that as the carbon granules'are compressed in one of them, the pressure on the granules of the other cell is reduced: Attachedin a suitable manner to the upper'end of the armature 10 are the two aluminum extensions -13 and 14 which are so -shaped as toavoid the extension 16"and grasp securely the pin connecting" together the movable electrodes of the two microphone "cells. It is now apparent that movement of the armature 10 operates the two microphonecells diflerentially. The two microphone'cells 12 are held in position by the two'brack'ets 15 secured-to the sidesloftheframe. I v Y H In'order to give stability to each microphone cell, I have provided the movable'electro'de 20 having-a difieren't slope from that given'to the stationary electrode 21 so that at-the center-the distance between the electrode surfaces will 'be greater than at the outer edges. By this arrangement the carbon granules,which occupy barely half of the cell, are kept from packing'and, thereby, deadening the cell. This construction is best seen in'the enlarged view of the micro phone cell in Fig.2. Q l I Referring to Fig. 1, I will nowdescribe the electrical circuitof the amplifier. The alternating current coils's carried by the cores 7 are serially connected inthe input circuit 22 over which is received the current of'audible frequencies to be amplified. The 'mag'netically centered armature 10 is vibrated by coils 8 within the working air gap between the two cores 7 in synchronism with the alternations of the current in the input circuit 22 due to the action of the coils in changing the fluxes in the airgaps-between the armature and the cores; Because of the differential action of the coils, the flux in one air gap is-iricreased and simultaneously the flux in the other air gap is decreased and vice versa. These changes in flux density cause the vibration of the armaturebetween the two magnet, poles. v,This vibration of the armature 10 manipulates the two cells 12 difierentially, re-

:sulting in undulations in the direct current cir- .euit corresponding to the current alternations in the'input circuit. By means of the induction coil ;I these'undulations cause alternating current to be induced in the output circuit 23. This output current-corresponds in wave form to the input current, varying therefrom in intensity only, the

amplifier.

-"Becau'seof this true amplification by my amplifier, it is now'possible to connect two or more of the' amplifiers of this character in tandem and obtain a resultant current which is substantially free from distortions Heretofore, this has been impossible since, because ofthe inherent tuning characteristic-"oi thespring-centered type of polarized "relays" used in electro-mechanical a'mplifiers',= each' stage 'of amplification addi= tionally distorted the original voice waves until, after a veryfew'stages, the reproduction was so distorted as tobe iridistinguishablei Summarizing the foregoing' the amplifier of myinvention comprises a differential polarized electromagnetmechanically connected to a differential microphone cell and battery-circuit and that-the inherent tuning characteristic of nowknown eleetro-mechanical amplifiers has been eliminated by supplanting the armature centering orrestoring spring'with a magnetic centeringarr'angement, thereby reducing the natural frequency of the device to a point where it is negligible when used with currents of audible frequencies.-

Having thus described my invention, what I considernew and desire to have protected by Letters Patent is described in the'claims which foll'ow."--

What is claimed is:

' 1; In a polarized relay, a polarizing magnet, an

armature disposed between the poles'ther'eofya pair ofelectromagnetshaving cores also disposed on'either side of said armature between equidistant from both cores; I

' 2. In' a polarized-'relay a polarizing magnet,

-an armature disposed between the poles thereof and pivotal contact with one pole, a pair of electromagnets having cores disposed between said'poles and"rigidly secured to said- 'one'pole,

whereby parallel paths for the "flux between said poles" are provided in said'cores' and armature,

the flowing through said armature being normally greater than that through eithercore and normally tending to hold the armature equidistant from bothcoresn I 1 3 In a polarized relay, a polarizing magnet, an '-armature'"disposed between the'poles thereof and in: pivotal contact with" one pole, there being 'an air gap betweenthefree end' of said armature and the otherpole, a pair of electromagnets having c'oresf shorter-than said armature disposed between said *poles and'rigidl'y secured to said one pole,sa id' cores being one on each side of said armaturegand forming an' air gap atftheir free ends in which said armature is located; said cores and armature forming paths for the flux between said poles, the fluxes in said cores converging with flux in said armature at the free ends thereof, whereby the normal flux between said poles tends to maintain said armature equidistant irom both cores.

4. An electromagnet comprising a permanent magnet, a pair of coils having cores immovably secured to the same pole of the permanent magnet and disposed with the free ends of the cores opposite each other with an air gap therebetween, an armature pivoted on said same pole and extending between said free ends or said core within said air gap, and means for maintaining said armature disposed equidistantly with respect to said free ends of said cores at said air gap when only the normal magnetic force exists thereat, said means comprising a pole piece attached to the other pole of the permanent magnet and disposed adjacent the free end of the armature.

5. In a polarized relay, a polarizing magnet, an armature pivotally connected to one pole of said magnet and having its free end in close proximity to the other pole of said magnet so that the attractive force of said other pole tends to maintain said armature in a predetermined position with respect to said polarizing magnet, and a pair of auxiliary pole pieces also extending from said one pole into close proximity with opposite sides of said armature, said pole pieces serving to lead into the armature at that point two magnetic fluxes which are adjusted to substantial equality of pull on the armature, such slight difierence as may exist being slightly more than offset by the attractive force of said other pole.

6. In a polarized relay, a polarizing magnet, an armature pivotally connected to one pole of said magnet and having its free end in close proximity to the other pole of said magnet so that the attractive force of said other pole tends to maintain said armature in a predetermined position with respect to said polarizing magnet, a pair of auxiliary pole pieces also extending from said one pole into close proximity with opposite sides of said armature, said pole pieces serving to lead into the armature at that point two magnetic fluxes which are adjusted to substantial equality of pull on the armature, such slight difference as may exist being slightly more than offset by the attractive force of said other pole, and difierentially connected windings on said auxiliary pole pieces adapted, when supplied with alternating current, to differentially destroy said equality of pole-piece fluxes to thereby cause said armature to vibrate in synchronlsm with the current alternations.

'7. In a polarized relay, a polarizing magnet, an armature disposed between the poles thereof, said armature being in pivotal contact with one pole and separated from the other pole by a small air gap, a pair of cores of magnetic material rigidly secured to said one pole and disposed one on each side of said armature, said cores extending substantially parallel with said armature a portion of their lengths and converging at their free ends to form an air gap through which said armature extends for a portion of its length, said cores and said armature providing paths for the flux between said poles, the major portion of the flux in each core joining the flux in said armature where said cores converge, thereby strongly polarizing said armature, a pole piece secured to said other pole and having an extension corresponding in end area to the end area of said armature and disposed directly opposite the free end of said armature, whereby the flux is concentrated and a magnetic force is provided to center said armature in the air gap between the core ends, and alternating current coils on said cores adapted to be diiferentially connected in an alternating current supply circuit, whereby the fluxes in the air gaps between the core ends and said armature are differentially affected when alternating current flows through said coils and said armature is vibrated in said air gap in synchronism with the current alternations.

8. In a magnetic device, a polarizing magnet, a pair of electromagnets having their cores secured to one of the poles of said magnet and disposed in the flux path between said poles to provide metallic paths for the flux a portion of the distance between said poles, an armature disposed between said poles and likewise between said cores and in pivotal contact with said one pole thereby providing a third path for the flux, the flux in said armature being greater than that in each core and tending to normally maintain the armature equidistant from said cores, and a microphone cell mechanically connected to said armature so as to be afiected by a movement of said armature towards either of said cores.

9. In a magnetically operated device, the combination of a vibratory electrode, a vibratory armature connected to the electrode so as to act in opposite directions thereon, a pair of oppositely acting electromagnets for differentially acting upon said armature, and a polarizing magnet connected to the cores of said pair of magnets and said armature in such a manner that the normal magnetic flux normally maintains said armature neutral with respect to said pair of magnets, thereby normally tending to maintain said electrode in its neutral position.

10. In a magnetic device, the combination of an element to be vibrated, a vibratory armature connected to the element, a pair of electromagnets having their cores disposed one on either side of said armature and in close proximity thereto for differentially acting upon said armature, and a polarizing magnet having one of its poles connected to said cores and said armature, whereby the magnetic flux normally maintains said armature neutral with respect to said cores thereby normally maintaining said element in its neutral position.

11. In a magnetic device, a polarizing magnet, an armature having one end pivoted on one pole of said magnet and the other end in close proximity to the other pole of said magnet, a pair of electromagnets, a core for each electromagnet having one end secured to said one pole of said magnet, the other end of each core being in close proximity to said armature, said cores and said armature providing parallel paths between said poles, the flux flowing through said armature being normally greater than that flowing through either core and the flux flowing through said cores exerting a repelling action on said armature whereby the flux holds the armature equidistant from both said cores.

ARTHUR BESSEY SMITH. 

